Kenya police shot dead a street vendor as opposition supporters held demonstrations calling for electoral reform, a senior police official said Monday, while human rights groups said police had killed dozens of people who protested after August's now-annulled presidential election.

The government last week banned opposition protests in the business districts of Kenya's three largest cities, but they have continued. Police on Monday prevented protesters from entering Nairobi's central business district. The street vendor was shot dead in the western city of Kisumu. The senior police official spoke on condition of anonymity because he was not authorized to speak to reporters.

"The police came and beat him with sticks badly and then they came and shot him at close range in the back," protester Jackson Juma told The Associated Press.

Amnesty International and Human Rights Watch said as many as 67 people died across the East African nation after President Uhuru Kenyatta's re-election was announced. The Supreme Court later nullified the vote, citing irregularities, and a new election is Oct. 26.

Supporters of Raila Odinga demonstrated Monday in Kisumu, Kenya to demand the removal of officials from national election oversight body they say has not been sufficiently reformed since the Aug. 8 presidential elections were annulled. (Yasuyoshi Chiba/AFP/Getty Images)

Human Rights Watch and Amnesty said police in Nairobi had used "excessive force" and that "most of [the 33 who died in Nairobi] were killed as a result of action by the police."

Among them was a nine-year-old child shot dead while standing on a balcony and a woman who was eight months pregnant and was trampled to death after fainting from inhaling tear gas, the rights groups said in the report.

Many operations alleged in Nairobi slums

Researchers from the two groups interviewed 151 victims, witnesses, police and others in Nairobi's low-income areas known to be opposition strongholds. The report said security agents carried out operations in Mathare, Kibera, Babadogo, Dandora, Korogocho, Kariobangi and Kawangware slums between Aug. 9 and 13.

"This deadly use of excessive force has become a hallmark of police operations in Kenya and must be decisively stopped before the next election takes place," said Michelle Kagari, a deputy regional director with Amnesty International.

Opposition supporters protesting over the upcoming elections, and passersby, run from a cloud of tear gas fired by riot police in downtown Nairobi, on Monday. (Khalil Senosi/Associated Press)

National police spokesman George Kinoti rejected the report, describing it as "sensational" and based on "falsehoods."

Opposition leader Raila Odinga, whose legal challenge of vote-rigging had led the court to nullify the election, later withdrew his candidacy for the new vote. He said his calls for reforms of the electoral commission have been ignored, and he called for supporters to hold daily protests this week.

Ethnic violence led to the deaths of over 1,000 people after the 2007 vote. Odinga ran unsuccessfully in that election; he also lost the 2013 vote to Kenyatta and took allegations of vote-tampering to Kenya's highest court, which rejected his case.